The majority of volcanic products on Mars are thought to be mafic and effusive1,2. Explosive eruptions of basic to ultrabasic chemistry are expected to be common3,4, but evidence for them is rare and mostly confined to very old surface features5. Here we present new image and topographic data from the High Resolution Stereo Camera that reveal previously unknown traces of an explosive eruption at 30° N and 149° E on the northwestern flank of the shield volcano Hecates Tholus. The eruption created a large, 10-km-diameter caldera ∼350 million years ago. We interpret these observations to mean that large-scale explosive volcanism on Mars was not confined to the planet's early evolution. We also show that glacial deposits partly fill the caldera and an adjacent depression. Their age, derived from crater counts, is about 5 to 24 million years. Climate models predict that near-surface ice is not stable at mid-latitudes today6, assuming a thermo-dynamic steady state. Therefore, the discovery of very young glacial features at Hecates Tholus suggests recent climate changes. We show that the absolute ages of these very recent glacial deposits correspond very well to a period of increased obliquity of the planet's rotational axis7.
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We thank the entire HRSC experiment and instrument teams at the German Aerospace Center (DLR) and at the Freie Universität Berlin, as well as the Mars Express teams at ESTEC and ESOC. This study would not have been possible without their work. In particular, we appreciate the support of H. Hoffmann, T. Roatsch, K.-D. Matz, V. Mertens, J. Flohrer, R. Pischel, F. Scholten and K. Gwinner. HRSC was developed at DLR and industrial partners. G.N. is the Principal Investigator of this experiment. We are grateful to U. Wolf for her support in crater counting. M. Aittola, J. Korteniemi, P. Kostama and D. Williams supported the HRSC image planning. T. Lowell provided an image of his collection of glacier photographs. Comments by J. Helbert helped to improve the manuscript.
The authors declare that they have no competing financial interests.
A list of all members of The HRSC Co-Investigator Team and their affiliations appears at the end of the paper
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Hauber, E., van Gasselt, S., Ivanov, B. et al. Discovery of a flank caldera and very young glacial activity at Hecates Tholus, Mars. Nature 434, 356–361 (2005). https://doi.org/10.1038/nature03423
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